1. Field of the Invention
The present invention relates to a gas turbine combustor and a fuel supply method therefor.
2. Description of the Related Art
Gas turbine combustors need, as a critical requirement, to provide stable combustion for a period of time ranging from starting-up to rated load operation even if operating conditions such as an air flow rate, a fuel flow rate and the like significantly change. Also a combustion method is strongly demanded in which a discharge amount of nitrogen oxide discharged from a gas turbine combustor is decreased. Nitrogen oxide will be referred as NOx hereinafter.
A premixed combustion method is one example of combustion methods allowing a less NOx discharge amount to be discharged. The premixed combustion method is such that fuel is mixed with air prior to combustion reaction and the mixture is then burnt. In general, a NOx amount is exponentially increased as combustion flame temperature is made high. However, if the premixed combustion method is used for gas turbine combustors, a local increase in combustion flame temperature can be prevented from occurring. Further if the ratio of air to fuel is increased so that premixed gas is made lean, the combustion flame temperature can be decreased. As a result, reduction in an amount of NOx discharge can be achieved.
To cope with an increasing strong demand for NOx reduction, opportunity of operating a combustor based on a lean premixed combustion, in which a premixed gas is made far leaner, has recently increased when the premixed combustion method is applied. However, the lean mixed combustion generally has following characteristics: flames are more likely to blow off than those in diffusion combustion in which air and fuel are burnt while they are mixed with each other, and combustion oscillation is liable to occur. Therefore, the premixed combustion method has a limited operational range where stable combustion is possible.
In view of the above, the lean premixed combustion method is combined with the diffusion combustion method having high combustion stability to promote reduction of NOx while the stabilization of combustion is ensured.
JP-11-101435-A describes a method of suppressing the sway of flames, which is formed by a diffusion combustion burner even when a flow rate of fuel to be supplied to the diffusion combustion burner is reduced for the purpose of reducing a NOx discharge amount.